The invention relates to a method and system for monitoring fluid flow in a conduit.
A variety of flowmeters is currently available to monitor fluid flow in a conduit. Many existing flowmeters are costly pieces of equipment that are difficult to install in a confined space, such as downhole in an oil and/or gas production or in a fluid injection well.
It is known from U.S. Pat. No. 6,378,380 to monitor in such case fluid flow by measuring a pressure difference across a flow restriction in the conduit. However, the installation and calibration of such a flowmeter in an oil and/or gas production or in a fluid injection well is still a complex and costly operation.
A further disadvantage of existing in-well venturi flowmeters is that delta-P (Δp) sensors are not available for downhole use and that therefore absolute pressure gauges to be installed upstream and downstream of each venturi meter. The consequence is that to derive at a downhole delta-P (Δp) measurement two large numbers have be subtracted which is a large source of inaccuracy.
To reduce this inaccuracy, usually a downhole venturi is usually designed with a large beta (i.e. a small inner diameter) to increase the pressure drop (Δp). The large pressure drop (Δp>1 bar) inhibits the fluid flux and the small inner diameter of the venturi may prevent logging tools to pass the venturi. To permit use of a venturi with a relatively large inner diameter to measure a relatively small delta-P, which requires selection of highly sensitive pressure gauges (like quartzdyne gauges), which are very expensive. Furthermore, each pressure gauge has a defined operating range (often 1:10) resulting in a relatively small operating range of the venturi flow meter (1:3). The selection of pressure gauges for downhole use therefore requires a good understanding of possible variations of the expected downhole pressures and pressure drops (Δp) throughout the life time of the well.
There is a need to avoid or alleviate the limitations associated with the conventional Δp measuring method.
Furthermore there is a need for a method and system for monitoring fluid flow at multiple points in a conduit in a cost effective manner, without the need to install pressure gauges and other associated costly equipment.